MEXICO: In 1834, Charles Darwin discovered a very strange set of bones as his famous HMS Beagle was surveying the area around Port St. Julian in Patagonia, or what is now Argentina.

At first, Darwin identified the fossils as belonging to a large animal resembling a mastodon. But later, working with anatomist Richard Owen, he discovered that the creature’s vertebrae and other bone fragments were more similar to those of some gigantic camel-like species. Owen named the creature M...